Reference is made to FIG. 1 showing a circuit diagram for a basic switching regulator circuit 10. The circuit includes a supply voltage 12 having a first (more positive) node 14 and a second (more negative or ground) node 16. A transistor switch 18 (in this example, an n-channel MOSFET device) has its current conduction path (the source-drain path) coupled between the node 14 and an intermediate node 20. The control terminal (the gate) of the transistor switch 18 receives a pulse width modulated (PWM) control signal generated by a control circuit 22. A diode 24 is connected between the intermediate node 20 and the ground node 16 (with the anode terminal coupled to the node 16 and the cathode terminal coupled to the node 20). It is understood by those skilled in the art that the diode 24 could instead be replaced with a transistor switch (such as an n-channel MOSFET device) that is controlled by an appropriate phase of the PWM control signal if desired. An inductor 26 is coupled between the intermediate node 20 and an output node 28. A current sensing circuit 30 may be used to sense current flowing in the inductor 26, with that sensed current used by the control circuit 22 in generating the PWM signal to regulate the output. A voltage sensing circuit 32 may be used to sense voltage at the output, with that sensed voltage used by the control circuit 22 in generating the PWM signal to regulate the output. A capacitor 34 is coupled between the output node 28 and the node 16 in parallel with a load 36. The PWM signal has a fixed frequency, but a variable duty cycle set by the control circuit 22.
The general configuration of the PWM signal is shown in FIG. 2. During a first phase 40 of a PWM cycle of the PWM signal, the transistor switch 18 is turned on and current flows from the supply voltage 12 through the inductor 26 to charge the capacitor 34. The current through the inductor 26 increases during this phase 40. During a second phase 42 of the PWM cycle, the transistor switch 18 is turned off and the supply voltage 12 is disconnected from the inductor 26. The diode 24 becomes forward biased and the inductor current flows through the load 26. The current through the inductor 26 decreases during this phase 42. The current flow waveform for inductor current is shown in FIG. 3.
In some instances, a measurement of the average current (Iav) flowing through the inductor is an important operational characteristic to know. What is needed in the art is a circuit and method for measuring average inductor current.